McMillan Model of the Superconducting Proximity Effect for Dilute Magnetic Alloys

Abstract

We extend the tunneling model of McMillan for the proximity effect in normal-superconducting sandwiches to the case when the normal metal film contains magnetic impurities. The excitation spectrum in each film and the superconducting transition temperature of the sandwich are calculated as functions of the impurity concentration and the film thickness. For a large range of impurity concentrations, the calculations predict that the density of states in both films is gapless, although the transition temperature of the sandwich is nonzero. The calculations are considered in relation to experiment, with reference to possible experimental probes for the Kondo effect in alloys which are nonsuperconducting in the bulk.